Polymer degradation

ABSTRACT

Methods of degrading a polymer into oligomers and/or monomers in a solvent, using a catalyst, and a functionalized magnetic particle comprising a catalyst being capable of degrading the polymer into oligomers and/or monomers are disclosed. The method and particle provide a high selectivity and a high conversion ratio.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Stage of International Patent Application No.PCT/NL2015/050907′ filed Dec. 23, 2015, which claims the benefit of andpriority to Netherlands Application No. 2014048, filed Dec. 23, 2014 andNetherlands Application No. 2014050, filed Dec. 23, 2014, all of whichare incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

The present invention is in the field of a method of degrading a polymerinto oligomers and/or monomers in a solvent, using a catalyst, and afunctionalized magnetic particle comprising a catalyst being capable ofdegrading the polymer into oligomers and/or monomers. The present methodand particle provide a high selectivity and a high conversion ratio.

BACKGROUND OF THE INVENTION

With respect to degradation of used polymers (or plastics), typicallypresent as a product or material, it is noted that in general this ishindered by lack of separation methods (e.g. separation of a firstpolymer from a second polymer, such as polyethylene (PE) andpolypropylene (PP)). As a consequence a significant amount of usedpolymers is used as a fuel, which is burned.

It is noted that chemical recycling of polymers such as Polyethyleneterephthalate (PET) is considered cost-efficient only applyingrelatively high capacity recycling lines of e.g. more than 50ktons/year. Most likely such lines will only be combined with productionsites of very large polymer producers. Several attempts of industrialmagnitude to establish such chemical recycling plants have been made inthe past but without resounding success. Even the promising chemicalrecycling in e.g. Japan has not become an industrial break through sofar; there seem to be two main reasons therefore: first, a difficulty ofconsistent and continuous waste bottles sourcing in a required hugeamount at one single site, and, at second, the steadily increased pricesand price volatility of collected bottles. So despite huge amounts ofPET produced on a yearly basis (>50.000 ktons) forming similar amountsof waste no economically feasible process has been introduced.

A further issue is that if a separation is (partly) successful,degradation into smaller building units still is difficult. Many methodsor processes are not selective enough, that is a discrimination, shownby a reagent in competitive attack on two or more substrates or on twoor more positions in the same substrate, is relatively low. It istypically quantitatively expressed by ratios of rate constants of thecompeting reactions, or by the decadic logarithms of such ratios.Further a conversion is too low; efficient conversion of reactants(polymers) to desired products (monomers or oligomers) without muchwastage production in terms of side products is an issue. As aconsequence a yield, being regarded as a product of selectivity timesconversion, is too low as well.

A problem with a use of catalysts, especially free catalysts in asolvent, is that it is virtually impossible to recover the catalystafter a first usage. As catalysts are typically quite expensive, onewould like to recover a catalyst, at least largely, and reuse thecatalyst a second time and preferably many more times. A small waste ofcatalyst would be acceptable, if a waste is in the order of a fewpercent or less. In this respect Wang (in Wang et al, “Fe-containingmagnetic ionic liquid as an effective catalyst for glycolysis ofpoly(ethylene terephthalate)”, Cat. Comm. 11 (2010), pp. 763-767, and inEur. Pol. J., Pergamon Press Oxford, vol. 45, no. 5, 1 May 2009, pp.1535-1544), and Xueyuan Zhou et al. (in Pure and Applied Chemistry, Vol.84, No. 3, 1 Jan. 2012, pp. 789-801) mention degradation of PET using acatalyst, without reusing the catalyst and with moderate results. Theamount of catalyst used in these processes is relatively high (17-80 wt.%. catalyst per weight PET) and results are far from optimal.

Further it is in general considered a disadvantage to combine a catalystto a support. Amongst others selectivity and conversion, as well asavailable catalyst are jeopardized. As such compared to non-combinedcatalyst typically more catalyst needs to be used in order to obtainsimilar results, and even then selectivity and conversion are stillworse. In this respect Valkenberg et al. in “Immobilisation of ionicliquids on solid supports”, Green Chemistry, 2002 (4), pp. 88-93, showsionic liquids attached to solid supports, e.g. a metal oxide, such asTiO₂, SiO₂, Al₂O₃, etc. Lee in “Functionalized imidazolium salts fortask-specific ionic liquids and their applications”, Chem. Commun.,2006, pp. 1049-1063 mentions similar catalysts. Such relate to atwo-phase system. The results of the catalytic activity tested areconsidered rather poor, apart from some exceptions, especially in termsof conversion and selectivity. Valkenberg, in table 3 shows a comparisonbetween an Fe-IL in unsupported status and in supported status. Foranisole the conversion drops from 90% to 6.5% (or about 30% forcharcoal) and for m-xylene it drops from about 34% to 15% (or about 18%on charcoal). So a macroscopic support would typically not be consideredfor an ionic liquid in view of conversion. It is found important tofurther optimize reaction conditions. In other words the catalysts on asupport would not be considered to be used.

In general most catalysts are used for synthesis of molecules and thelike, not for degradation. Typically catalysts, and especially catalystcomplexes, and function of a catalyst are sensitive to contaminantsbeing present; in other words they function only properly under relativepure and clean conditions. As a result of contamination catalysts needto be replaced regularly, and extreme care is typically taken not tointroduce contaminants. That may also be a reason why catalyst aretypically not considered for degradation processes, as these processesalmost inherently introduce contaminants.

In some instances metal catalysts are directly attached to ananoparticle. Such catalysts are typically used for synthesis, but notfor degradation, and certainly not for a reaction with at least onesolid reactant. In this respect it is noted that for synthesis areaction between two or more components is executed, wherein the two ormore components are in close contact, such as in a solvent. The natureand relevant parameters of a synthesis reaction is considered to bequite different from degradation reactions; for instance relative lowamounts of catalyst may be used and relatively high yield may beobtainable under optimal conditions. One can therefore not expect theteachings of synthesis reactions to be applicable in general todegradation reactions.

Reactions can take place in various types of reactors. In flowchemistry, a chemical reaction is run in a continuously flowing streamrather than in batch production. In other words, pumps move fluid into atube, and where tubes join one another, the fluids contact one another.If these fluids are reactive, a reaction takes place. Flow chemistry isa well-established technique for use at a large scale when manufacturinglarge quantities of a given material. Often, microreactors are used.

Various patent documents and scientific documents recite fluidscomprising magnetic particles.

Magnetic Fluids are a class of smart materials that change theirproperties reversibly and relatively fast (milliseconds) under presenceof an external magnetic field. These fluids can show changes in apparentviscosity of several orders of magnitude when a magnetic field isapplied, such as a magnetic flux density in the order of around 1 T.

The present invention provides an improved method for degrading polymerstypically present in a polymer material which overcomes at least one ofthe above disadvantages, without jeopardizing functionality andadvantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to an improved methodaccording to claim 1, showing partly major improvements over the priorart, e.g. in terms of selectivity (93% versus 59.2%), conversion, yield,a very low amount of catalyst used per amount of productdegraded/obtained (0.2-18 wt. % versus 17-80 wt. % [weightcatalyst/weight polymer]), use of energy (1 hour versus 4 hours; so alsomuch quicker), insensitivity to contaminants, such as environmentalsubstances, such as environmental substances, insensitivity tocomposition of raw material (i.e. the type of polymer to be degraded andthe type of additive), etc. Put in numbers, the present inventionprovides a conversion of about 100%, a selectivity of significantly morethan 90% (versus some 59.2% prior art), reuse of catalyst (over 50times, being absent in prior art degradation processes), allowing anymixture of waste polymers (not known in the prior art, typically wellcleaned, well separated, having one type/source of material, is neededfor prior art processes), a relatively modest temperature and pressuremay be used (200° C. versus e.g. 350° C.), etc. It is noted that thepresent catalyst complex shows an improved localized action. It is alsonoted that typically improvement in one aspect (parameter) involves adeterioration in another aspect (parameter); the present range ofimprovements in various aspects together is already in that sensesurprising.

For various details of the present method and catalyst complex usedtherein reference is made to the International ApplicationsPCT/NL2014/050418, and WO2014/142661 A2, filed by the same applicant,which contents are incorporated by reference.

The present catalyst complex comprises three distinguishable elements: ananoparticle, a bridging moiety attached, such as by a covalent bond, tothe nanoparticle and a catalyst entity (chemically, such as by acovalent bond) attached to the bridging moiety. The bridging moiety issolely in between the catalyst and the nanoparticle, respectively. Thepresent complex is for instance different from a complex having abridging moiety fully covering a nanoparticle, such as in a core-shellparticle.

The present nanoparticle is of a magnetic nature. As such nanoparticlescomprising a magnetic material are included, as well as particles thatcan be magnetized sufficiently under relative modest magnetic fields,such as being applied in the present method. The use of magneticnanoparticles has the advantage that these may for instance be recoveredby magnetic attraction after use. Suitably, the magnetic nanoparticlescontain an oxide of iron, manganese and/or cobalt, or combinationsthereof. Iron oxide, for instance but not exclusively in the form ofFe₃O₄ is preferred. Another suitable example is CoFe₂O₄.

It has been found that the nanoparticle should be sufficiently small forthe catalyst complex to function as a catalyst, therewith degrading thepresent polymer into smaller units, wherein the yield of these smallerunits, and specifically the monomers thereof, is high enough forcommercial reasons. It is noted in this respect that a commercial valueof waste polymers to be degraded is relatively small, i.e. a costs ofdegrading should be small as well. It has further been found that thenanoparticle should be sufficiently large in order to be able to reusethe present complex by recovering the present catalyst complex. It iseconomically unfavorable that the catalyst complex would be removed witheither waste or degradation product obtained. Suitable nanoparticleshave an average diameter of 2-500 nm. It is preferred to usenanoparticles comprising iron oxide. The catalyst entity, beingselected, can then be attached to the present magnetic nanoparticles.

The present catalyst entity comprises at least two moieties. Such hasbeen found to contribute to at least some of the present advantages. Afirst relates to an aromatic moiety having a positive charge (cation). Asecond relates to a moiety, typically a salt complex moiety, having anegative charge (anion). The negative and positive charge typicallybalance one and another. It has been found that the positively andnegatively charged moieties have a synergistic and enhancing effect onthe degradation process of the polymer in terms of conversion andselectivity, especially in view of degrading polyesters and polyethers.

The aromatic moiety preferably comprises a heterocycle, having at leastone, preferably at least two nitrogen atoms, such as an imidazole,preferably butylmethylimidazolium (bmim⁺), ethylimidazolium, orbutylimidazolium (bim⁺). The aromatic moiety preferably stabilizes apositive charge. The heterocycle may have 5 or 6 atoms, preferably 5atoms. Typically the aromatic moiety carries a positive charge. If anitrogen is present the charge is on the nitrogen.

The negatively charged moiety (anion) may relate to a salt complexmoiety, preferably a metal salt complex moiety, having a two- orthree-plus charged metal ion, such as Fe³⁺, Al³⁺, Ca²⁺, and Cu²⁺, andnegatively charged counter-ions, such as halogenides, e.g. Cl⁻, F⁻, andBr⁻. In an example the salt is an Fe³⁺ comprising salt complex moiety,such as an halogenide, e.g. FeCl₄ ⁻. Alternatively, use can be made ofcounter-ions without a metal salt complex, such as halides as known perse.

The present catalyst entity and nanoparticle are combined by a bridgingmoiety. The person skilled in the art would expect that binding acatalyst entity, such as one according to the invention, onto a supportwould jeopardize the functioning of the catalyst entity, at least tosome extent. In this respect the present nanoparticle is not consideredto be a support. Surprisingly, the present bridging molecule incombination with the nanoparticle provides a catalyst complex whichfunctions almost as good as or better than the catalyst entity itself.For performance of the process in terms of conversion, selectivity, andeconomical feasibility the above needs to be taken into account;otherwise no effective degradation is obtained, e.g. in terms ofconversion, selectivity, and economical feasibility. The presentbridging moiety provides the above characteristics (in addition to thepresent nanoparticle). It is noted that up to now no economically viableprocess for polymer degradation has been provided.

In an example of the present catalyst complex the magnetic particleshave an average diameter of 2 nm-500 nm, preferably from 3 nm-100 nm,more preferably from 4 nm-50 nm, such as from 5-10 nm. As indicatedabove, the particles are preferably not too large and not too small. Ithas been found that e.g. in terms of yield and recovery of catalystcomplex a rather small size of particles of 5-10 nm is optimal. It isnoted that the term “size” relates to an average diameter of particles,wherein an actual diameter of a particle may vary somewhat due tocharacteristics thereof. The size is determined per individual particle.In addition aggregates may be formed e.g. in the solution. Theseaggregates typically have sizes in a range of 50-200 nm, such as 80-150nm, e.g. 100 nm. Particle sizes and a distribution thereof can bemeasured e.g. by light scattering, e.g. using a Malvern Dynamic lightScattering apparatus, such as a NS500 series. In a more laborious way,typically applied for smaller particle sizes and equally well applicableto large sizes representative EM-pictures are taken and the sizes ofindividual particles are measured on the picture. For an average anumber weight average may be taken. In an approximation the average maybe taken as the size with the highest number of particles or as a mediansize.

In an example of the present catalyst complex the bridging moiety isprovided in an amount of (mole bridging moiety/gr magnetic particle)5*10⁻⁶-0.1, preferably 1*10⁻⁵-0.01, more preferably 2*10⁻⁵-10⁻³, such as4*10⁻⁵-10⁻⁴. Attached to each bridging moiety is typically a catalystmoiety, typically by a chemical covalent bond. The bridging moiety isalso typically attached to the nanoparticle by a covalent bond. It ispreferred to have a relatively large amount available in terms of e.g.yield, energy consumption, etc., whereas in terms of amount of catalystand costs thereof a somewhat smaller amount is available, especially asthe magnetic nanoparticles are considered as a relatively cheap part ofthe catalyst complex. Surprisingly the present method can be performedwith very low amounts of catalyst complex, compared to prior artmethods.

For the present method the solid polymer is provided in a suitablesolvent. As such the present method may be considered as a solid-liquiddegradation process supported by addition of a recoverable catalystcomplex. For a glycolysis the solvent is preferably a mono- ordi-alcohol, such as an alkanol or alkanediol, such as methanediol,ethanediol, and propanediol. As such the solvent also functions as areactant. Inventors have found that in view of recovery of the presentcatalyst complex not all solvents are suited. Some solvents form astable “dispersion” with the catalyst complex; in such a case in thestep of recovery a second solvent, e.g. functioning as washing agent,may be provided and the catalyst complex may then be recovered using anelectromagnetic field.

The method may be carried out batch-wise, continuous, semi-continuous,and combinations thereof. In one advantageous embodiment, the methodcomprises a first stage involving a pre-treatment and a second stage forfull or substantial completion of the degradation reaction.

The first stage is preferably carried out so as to maximize heattransfer to any components in the reactor, i.e. polymer, solvent andcatalyst complex, without giving rise to agglomeration. Said componentsare to be mixed to constitute a dispersion at elevated temperature.Preferably, use is made of a reactor provided with mixing means, such asa rotating mixer, that preferably is provided with mixing blades.Suitably, the reactor of the first stage is embodied to have arelatively short residence time, for instance less than 5 minutes,preferably at most 2 minutes.

In one embodiment, the heat is provided to the mixture by means ofsteam, preferably overheated steam. The steam may be led in a channelaround the reactor vessel, so as to heat the reactor vessel.Alternatively, or additionally, the steam may be led through the reactorand/or through an inner tube inside the reactor. Since the reactor is tobe heated to above 100° C., and preferably at a temperature and pressureat which the solvent remains liquid or could be boiling, liquefaction ofthe steam does not occur or occurs only to a limited extent. As aconsequence, the steam may be separated from the dispersion and thedispersion is not diluted significantly.

The second stage is preferably carried out in one or more plug flowreactors, so as to enable a proper contact between the catalyst complex,the polymer and the solvent. In one preferred implementation, the plugflow reactor comprises a plurality of tube-shaped reactor elements,which are arranged in parallel. The number of reactor elements arrangedin parallel is for instance in the range of 10-100, preferably 20-50.With this implementation, the wall of said tube-shaped reactor elementmay be used as a heating (or cooling) means, i.e. to maintain thedesired temperature. Furthermore, the tube-shape is deemed beneficialfor control of the pressure drop in the reactor, and therewith theresidence time. Moreover, the subdivision of the heated dispersion intoa plurality of tube-shaped reactor elements is deemed to ensure that theflow remains homogeneous.

According to a further aspect, the invention relates to such a reactorsystem having a first stage and a second stage, wherein the second stageis configured for plug-flow reaction by means of a plurality oftube-shaped reactor elements. This reactor system, as claimed in claim21, is most suitable for the catalyst complex as described hereinaboveand below, but may also be used for related catalyst complex, such ascatalyst complexes with another nanoparticle than a magneticnanoparticle. The invention further relates to the use of the reactorsystem of the invention for the degradation of the polymers, such aspolyesters.

The present method has a less selective feedstock, as from virginpolymer (such as PET) to various other recovered sources may beprovided. Also it provides a relatively low energy process. As aconsequence polymer produced from the present degradation products isconsidered to be ‘Green’ produced, such as in a case of PET up to 25%.

The present method can be considered to involve a dispersion, comprisinga solvent, a polymer to be degraded, and a catalyst complex. It is notedthat in general it is difficult to obtain a (time) stable dispersion. Inthis respect the present method distinguishes itself from a reactionwith a catalyst on a support, which effectively relates to a two-phasesystem, not being suitable for polymer degradation.

The temperature and pressure of the method may be adjusted. Typically asomewhat higher temperature is preferred in terms of reaction velocity;a lower temperature is preferred in terms of energy consumption.Likewise a higher pressure is somewhat preferred; in view of complexityof an installation a lower pressure is preferred, that is a pressurebeing about 100 kPa. It is an advantage of the present method that arelatively low temperature may be used, without jeopardizing yield. Itis also an advantage that using relatively mild temperature and pressureconditions the present degradation can be carried out in a relativeshort time. Such provides e.g. a relative high throughput, a relativelysmaller installation, and lower consumption of materials and energy.

It is a further advantage of the present method that the method isrelatively insensitive (e.g. in terms of yield) for mixed polymers beingprovided. Mixed polymers can relate to a combination of two or moredifferent types of polymers, such as different polyesters, such as PET,polyethylene furanoate (PEF), polytrimethylene terephthalate (PTT), andpolybutylene terephthalate (PBT), to a combination of one type ofpolymer having different properties, such as color, thickness, origin,and combinations thereof. Also the method is relatively insensitive tocontaminants, like additives being present in a polymeric composition,such as pigments, fillers, filters, are separated in the course of thedegradation process. It is understood by the inventors, that theadditives adhere to the catalyst complex. Particularly, the bridgingmoieties and catalyst entities jointly adhered to the nanoparticlesappear to enable adsorption of hydrophobic colorants. After thedegradation process, the catalyst complex may be regenerated, in thatthe additives are removed by washing. It was found in preliminaryinvestigations that degradation treatments of several batches ofpolyester bottles may be carried out before a washing step is needed.Mixed material comprising e.g. a polyester, such as PET, and a furthermaterial, such as a polyolefin, such as PE, a silicone material,polyamides, etc. can also be processed. As such the present method isconsidered robust, to be used under relatively sub-optimal conditions,such as in a plant.

Compared to prior art methods a characteristic of the present method isthat the catalyst complex is recovered. It is preferred to use thepresent catalyst complex in the present method.

Thereby the present invention provides a solution to at least one of theabove mentioned problems. The various examples and embodiments of thepresent invention described in relation to one aspect of the invention,are also deemed to be applicable to another aspect.

Advantages of the present description are detailed throughout thedescription.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a method according toclaim 1.

Within the present invention the term “polymer” typically relates to apolymer material or polymer product. In the present method the polymerproduct before processing has an average volume of 10⁻⁷-50 cm³,preferably 5*10⁻⁶-5 cm³, more preferably 5*10⁻⁵-0.5 cm³, even morepreferably 5*10⁻⁴-0.05 cm³. Such may require an extra process step ofreducing a size of polymer product provided, e.g. shredding PET-bottlesand grinding. A simple way of preventing too large polymer product partsis by using an appropriate sieve having a required mesh size, or asequence of sieves. It may be somewhat costly to pelletize or granulizepolymer; in view thereof somewhat larger pellets or granules arepreferred, or put different having a relative small surface/mass ratio.In view of e.g. yield and size of a plant smaller pellets or granulesare preferred. However, in view of environmental and health issuespellets or granules are preferably not too small. It is noted that alsopolymer bottles as such may be provided, possibly shredded to someextent.

The polymer concentration is from 1-40 wt. %, preferably from 2-30 wt.%, more preferably from 5-25 wt. %, such as 10-20 wt. %. In view of useof catalyst a somewhat higher concentration is preferred. In view ofdegrading a somewhat lower concentration is preferred. The polymer istypically provided in solid form. Preferably the plastic comprising thepolymer is fragmented into smaller pieces. It has been found that thepresent method and catalyst complex are also suited in methods whereinnatural fibres are degraded into smaller parts and/or are re-cycled,such as seed fibers, leaf fibers, bast fibers, skin fibers, fruit fibersand stalk fibers, such as cotton, kapok, sisal, agave, hemp, ramie,rattan, vine, jute, kenaf, wood, paper, wool, flax, bamboo and grass.

The average residence time of the polymer in the reactor during whichdegrading is performed is from 30 sec.-3 hours, preferably 60 sec.-2hours, more preferably 2 [min]-1 hours, such as 5 [min]-30 [min] Theshorter periods possible are considered relative short, especially ascompared to prior art processes. Depending on e.g. reactor size andboundary conditions longer or shorter periods may be used. For instance,a high pressure (500-3000 kPa) process at a temperature of 150° C.-350°C. leads to very short degrading times, in the order of minutes. Suchindicates that the present method, and catalyst complex used therein,provide a large degree of design freedom.

The reactor is selected from a (semi)continuous type, such as acontinuous stirred tank reactor (CSTR), and a tube-like reactor, such asa loop reactor, a plug flow reactor, an oscillatory flow reactor, anN-unit loop reactor system, and a batch type, and combinations thereof.

In an example of the present method degrading of the polymer isperformed in at least two stages, in the first stage the polymer ispre-treated, such as in a batch or (semi-)continuous mode, and in asecond stage the degradation is completed, such as in a tube-likesystem. An example of pre-treatment is homogenizing the PET in the EGsolution. Performing of the reaction in two stages provides theadvantage of a higher yield, less harsh reaction conditions, preventionof optional clogging, etc. In the context of the present invention theterm “stage” may refer to a process step, a reactor, a phase, andcombinations thereof.

In an example of the present method an average residence time of thepolymer in the second degradation stage is 10 sec-60 min, preferably 30sec.-30 min, i.e. relatively short.

In an example of the present method an average volume-metric residencetime (reactor volume/flow rate) of the polymer in de degradation step is10 sec-60 min, preferably 30 sec.-30 [min]

In an example of the present method the catalyst complex is provided asa first flow and wherein the polymer is provided as a second flow, orwherein the catalyst complex and polymer are provided in one flow. Suchoffers a high degree of flexibility, e.g. in adjusting an amount ofcatalyst.

In an example of the present method the degrading is performed at atemperature of 50° C.-500° C., preferably 90° C.-350° C., morepreferably 150° C.-250° C., even more preferably 170° C.-200° C., suchas 180° C.-195° C., e.g. 185° C. and 190° C. The preferred range isconsidered to relate to a relative mild temperature, especially ascompared to prior art processes which are performed at temperaturesabove 300° C. Even further, as the temperature applied is relativelymild, waste energy of an adjacent plant may be used for the presentprocess. It is noted that the present catalyst complex has been found tobe stable enough under the conditions mentioned, such as the abovetemperature. The present complex does not volatilize under the presentconditions.

In an example of the present method the amount of catalyst complex is0.1-35 wt. %, preferably 0.5-20 wt. %, more preferably 1-10 wt. %, evenmore preferably 2-7 wt. %, relative to a total weight of polymerprovided, such as (weight to weight) 1 ABC:15PET (:45 EG, ethyleneglycol). If the amount of catalyst is higher a shorter reaction time wasobtained, whereas at a lower amount longer reaction times were obtained.Depending on further boundary conditions one may vary the amount ofcatalyst. Here the amount of catalyst relates to the catalyst entity andbridging moiety, i.e. without nanoparticle.

The present capture complex may for instance be used in a ratio (weightto weight) of Complex:PET in a range of 1:5 to 1:500, such as 1:10-1:15.In addition the amount of e.g. ethylene glycol:PET may vary from 1:2 to1:20, such as 1:3 to 1:5. The waste polymers may relate to a single typeof polymer, such as PET, PEF, PA, etc., and also to a mixture thereof.It typically comprises 50-99.9 wt. % of a specific polymer, such as PET,the remainder being impurities, other polymers, other compounds, etc.

In an example of the present method the pressure is from 90 kPa-10.000kPa, preferably 100 kPa-8.000 kPa, more preferably 200 kPa-2.000 kPa.Mild pressures in an example are an advantage over some prior artprocesses, which need to be performed at relatively high pressures, ofe.g. 1000 kPa, often in combination with a high temperature.

In a selection of a combination of temperature and pressure a range of[T,P] from [180° C., 60 kPa] to [450° C., 8.200 kPa] may be chosen,preferably from [250° C., 420 kPa] to [400° C., 4.960 kPa], such as from[280° C., 790 kPa] to [350° C., 2.560 kPa]. For the combinations thedegradation time is found to be from 1.5 hours @[180° C., 60 kPa] toabout 20 seconds @[450° C., 8.250 kPa]. For safety reasons thedegradation is best carried out at a temperature below 350° C. and belowa pressure of 6.000 kPa, depending on the solvent.

In an example of the present method further comprises the step ofrecovering the catalyst attached to the magnetic particle using anelectro-magnetic field gradient, preferably in a magnetic field of 0.1-5T, preferably from 0.3-2 T, more preferably from 0.5-1.5 T, such as0.8-1.3 T, e.g. 1 T. Likewise alternative separation techniques, such asfiltering, centrifugation, etc. may be used. As such a relatively smallmagnetic field is found to be sufficient to recover the present catalystcomplex. In view of e.g. reactor design such is advantageous. In anexample water is provided, in order to separate the present complex fromthe present solvent. It has been found that it is much easier to removethe present complex from a water phase, than from the present solventphase. By providing a suited catalyst complex, such as the presentcomplex, the catalyst (complex) may be recovered. It has been found thattypically 95% of the catalyst complex can be recovered, and often even98-99%. As a consequence the present catalyst complex can be reused20-100 times, thereby e.g. saving costs. It has been found that arecovered catalyst complex functions equally well compared to a fresh(non-used) complex.

In an example of the present method further comprises the step ofrecycling the catalyst complex. After recovery the present complex canbe recycled to the present degradation process, or removed and e.g.stored for later use.

In an example of the present method further comprises the step ofremoving additives from the solvent, the additives being added to thepolymer when these where produced, such as colorants, fillers,anti-oxidants, etc. The additives may for instance be removed afteradding water and applying a magnetic field; in that case additives areeffectively separated from a phase wherein further the present catalyst,oligomers (typically having 4-12 monomers), trimers and dimers may bepresent. Such is advantages as in principle these additives are at thisstage not reused, whereas the degradation products are reused, possiblyformed into novel polymer.

In addition freed additives from the polymer may be captured by othercompounds, such as carbon black, especially in a further method steptypically performed after completion of the degradation.

In an example of the present method further comprises the step ofretrieving trimers, dimers, and/or monomers, preferably free ofadditives and contaminants, such as by chemical and/or physicalseparation, in one step, or in a combination of steps. In a first stepof retrieving e.g. water may be added. Monomers and solvent may dissolvein water, whereas catalyst complex, additives, oligomers, trimers anddimers, especially under influence of an external magnetic field, willform a separate phase. The catalyst complex, additives, oligomers,trimers and dimers may be reintroduced in a first reaction step, whereinthe polymer is degraded. In a second step of retrieving the monomers canbe retrieved by providing e.g. water, and then “crystallizing”. As suchthe degradation products are ready to be reused, in fact without afurther need to e.g. purify these products.

In an example of the present method the polymer is a mixture of wastepolymers, the mixture optionally comprising at least one of coloredpolymers. The present method is capable of handling waste polymers, andeven further a mixture of polymers, e.g. having differentcharacteristics, such as a different color. The yield of degradation hasbeen found not to be influenced noticeably. It is noted that prior artmethods at the most can only handle relatively pure waste polymer, andeven then results are discouraging.

In a further step an active compound, such as carbon black, may be addedto capture and remove remaining additives.

In an example of the present method the constituents such as solvent,catalyst complex and polymer, form a one-phase system. Such has beenfound advantageous, especially in terms of yield obtained. Also in termsof reactor design such is advantageous.

In an example of the present method the polymer may selected fromnatural polymers, biobased polymers, biodegradable polymers, polymersformed (directly or indirectly) from fossil fuels, and combinationsthereof. In an example the polymer is at least one of a polyester, apolyether, such as polyoxymethylene (POM), polyethyleneglycol (PEG),polypropyleneglycol (PPG), polytetramethyleneglycol (PTMG), polyethyleneoxide (POE), polypropylene oxide (PPO), polytetrahydrofuran (PTHF), andpolytetramethyleneetherglycol (PTMEG), a polypeptide, a polyamide, apolyamine, a polycondensate, preferably a polyester, such as polycarboxylic ester, wherein the poly carboxylic ester is preferablyselected from polyethylene terephthalate (PET), polyethylene furanoate(PEF), polybutylene terephthalate (PBT), polytrimethylene terephthalate(PTT), polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone(PCL), polyethylene adipate (PEA), polyhydroxyalkanoate (PHA),polyhydroxybutyrate (PHB), polyethylene naphthalate (PEN),Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and apolycondensate of 4-hydroxybenzoic acid and6-hydroxynaphthalene-2-carboxylic acid (VECTRAN). In other words a largevariety of polymers may be degraded by the present method. Someadjustments may be necessary, e.g. in terms of catalyst used,temperature applied, solvent used, etc. The present method is bestsuited for degradation of polyesters and polyethers.

In an example of the present method the solvent is a reactant, thereactant being capable of reacting with the polymer being degraded, andpreferably forming a mono- or di-ester with the monomer, such as analkanol and alkanediol, preferably methanediol, ethanediol, andpropanediol, water, and amino comprising reactants. In terms of e.g.reactor design and complexity of reaction such is an advantage. Further,a product obtained can e.g. in case of degradation of PET be directlyused as feed-stock for PET production.

In an example of the present method further comprises the step ofadjusting an amount of negative charged molecules (anions), such as byadding a salt, preferably a Fe³⁺ comprising salt, such as an halogenide,such as by adding FeCl₃. Surprisingly the yield of the present methodand the functioning of the catalyst complex can be maintained at a highlevel by adjusting an amount of the partly negatively charged moleculesused. Such is step is relatively simple to carry out, and costs thereofare considered minimal.

In an example of the present method further comprises the step ofproviding oligomers to the solvent, preferably oligomers produced by themethod. As such the oligomers may be degraded further, into dimers andmonomers, in a subsequent step. The subsequent step may be carried outin the same place as an initial step, e.g. in the same reactor.

In an example of the present method the magnetic particles are at leastone of ferromagnetic particles, antiferromagnetic particles,ferrimagnetic particles, synthetic magnetic particles, paramagneticparticles, superparamagnetic particles, such as particles comprising atleast one of Fe, Co, Ni, Gd, Dy, Mn, Nd, Sm, and preferably at least oneof O, B, C, N, such as iron oxide, such as ferrite, such as magnetite,hematite, and maghemite. In view of degradation yield magnetite andmaghemite are preferred magnetic particles. In view of costs, even whenfully or largely recovering the present catalyst complex, relativelycheap particles are preferred, such as particles comprising Fe.

In an example of the present method the bridging moiety is at least oneof a weak organic acid, such as a carboxylic acid, such as a C1-C18carboxylic acid, silyl comprising groups, such as silylethers, such astriethoxysilylpropyl, and silanol. For a weak organic acid the Katypically varies between 1.8×10⁻¹⁶ and 55.5. It has been found thatdespite negative expectations these bridging groups do not result in anon-acceptable reduced performance of the catalyst entity. Moreparticularly, the bridging moiety comprises a functional group forbonding to the nanoparticle and a second linking group to the catalystentity. The functional group is one of the groups as specifiedhereinabove, such as a carboxylic acid or a silicic acid (i.e. silanol)group. The linking group is for instance an alkylene chain, with thealkylene chain typically between C2 and C10, for instance propylene.

The bridging moiety is preferably combined with the catalyst entity inthe form of a reactant, in which the linking group is made reactive forchemical reaction with the catalyst entity, whereas the functional groupmay be protected. For instance, a suitable functionalization of thelinking group is the provision as a substituted alkyl halide. A suitableprotection of the functional group may be in the form of an ester or analkoxysilane. The reactant is thus for instance provided in the form ofa substituted alkyl halide, such as a trialkoxysilane-substituted alkylhalide, wherein the alkoxy is preferably methoxy or ethoxy and whereinthe alkyl is suitably C1-C6 alkyl, for instance propyl or butyl. In thisreaction, the alkyl-group will bond to a nitrogen-atom of theheterocyclic moiety, that gets positively charged in this manner. Thehalide forms the negatively charged counter-ion. The negatively chargedhalide may thereafter be strengthened by addition of a Lewis acid toform a metal salt complex. One example is the conversion of chloride toFeCl₄ ⁻.

Examples of suitable reactants include 3-propylchloride trialkoxysilane,3-propylbromide-trialkoxysilane, 2-propylchloride-trialkoxysilane,2-propylbromide-trialkoxysilane. The alkoxy-group is preferably ethoxy,though methoxy or propoxy is not excluded. It is preferred to usetrialkoxysilanes, though dialkyldialkoxysilanes andtrialkylmonoalkoxysilanes are not excluded.

In an example of the present method the aromatic moiety has at least onetail. The present tail relates to a tail like moiety. The at least onetail preferably having a length of C₁-C₆, such as C₂-C₄, the at leastone tail being attached to the at least one nitrogen atom. It has beenfound that for an optimal degradation a somewhat higher yield isobtained when the present tail is somewhat longer. In terms of mass ofcatalyst complex provided it has been found that a somewhat shorter tailis preferred.

In an example of the present method the magnetic nanoparticle comprises(per particle) at least one bridging moiety (B) and catalyst entity (C),preferably 2-10⁴ bridging moieties and catalyst entities (BC perparticle), more preferably 10-10³ bridging moieties and catalystentities (BC per particle). In principle, e.g. in view of yield, as manycatalyst entities as possible may be provided. However the amount ofcatalyst entities and there functioning is in view of e.g. degradationefficiency somewhat smaller than an amount that could be achieved. Alsowhen a larger particle is selected somewhat more catalyst entities maybe present.

In an example of the present method the amount of bridging moiety andcatalyst attached thereto is 0.03-99 wt. %, preferably 0.1-75 wt. %,more preferably 0.2-25 wt. %, even more preferably 0.3-10 wt. %,relative to a total weight of catalyst complex. Likewise as above, arelative low amount of 0.5-5 wt. % of catalyst entity has been found tobe optimal, such as 0.6-3 wt. %, within further boundary conditions suchas applied temperature. An amount of catalyst and/or bridging moiety maybe determined by TGA. It is noted that the present catalyst and bridgingmoiety may form a single (mono-) layer, or a part thereof not fullycovering the nanoparticle. Before applying the present catalyst complexin the present method it may be washed. The above weight percentages arerelative to a total weight of catalyst complex.

In an example of the present method the polymer and solvent, and thecatalyst complex, are provided at a temperature of 15-30° C., that is atambient temperature. Thereafter, in an example in a first stage thetemperature is increased to 170-200° C. as described e.g. above. Heatcan be provided by high pressure steam. The first stage can be in batchor (semi)continuous mode. If two stages are used, in the second stagethe temperature is maintained at 170-200° C. Heat can be provided byhigh pressure steam. The second stage can be in batch or(semi)continuous mode, such as a plug flow reactor. If one stage isused, the second stage is performed in the first reactor. In anotherexample the polymer and solvent are heated to 170-200° C. for 1-8 hours.Thereafter the present catalyst complex is added, possible at a slightlylower temperature 150-200° C. and depolymerization is performed during1-30 min. After completion of the reaction the mixture is cooled down to50-75° C. The released heat is scavenged and reused in the process. Atthis temperature separation occurs. Thereto heated water is provided tothe mixture. In an example a magnetic separation is applied, separatingthe present complex from the mixture. Other separation techniques may beused as well, such as filtration, and centrifugation. Thereafter themixture is cooled down further to 0-15° C.; at this temperaturecrystallization occurs. The released heat is scavenged and reused in theprocess. Thereafter the oligomers, trimers, dimers and/or monomers arecrystallized, and thereafter, optionally drying the obtained crystals,such as at a temperature of 40-75° C. Heat is provided, typically bereusing the heat scavenged. As an alternative the crystals may be driedin an excavator. As such the reaction products are obtained inrelatively pure form, and typically the major reaction product isbis(2-hydroxyethyl terephthalate (BHET) (>90%).

In an example of the present method the polymer is polyethyleneterephthalate (PET) or PEF, the solvent is ethanediol, the catalystcomprises butylmethylimidazolium (bmim⁺), ethylimidazolium (eim⁺), orbutylimidazole (bim⁺) and FeCl₄ ⁻, the bridging moiety is derived fromtriethoxysilylpropyl chloride (forming a propyltrisilanol), and thenanoparticle is magnetite and/or maghemite. The nanoparticles preferablyhave a size of 5-10 nm. The bridging moiety preferably is present in anamount of 10⁻⁴-10⁻² mole bridging moiety/gr nanoparticle, such as2*10⁻⁴-10⁻³. It is assumed that if a predetermined amount (moles) ofbridging moiety is attached to a predetermined amount (gr) practicallyall of the bridging moieties attach to the nanoparticle andsubstantially stay attached during the present method. Such isespecially a preferred embodiment in view of the abundant amount ofwaste PET being available, being in excess of hundreds of thousand tonsper year.

The invention is further detailed by the accompanying figures andexamples, which are exemplary and explanatory of nature and are notlimiting the scope of the invention. To the person skilled in the art itmay be clear that many variants, being obvious or not, may beconceivable falling within the scope of protection, defined by thepresent claims.

SUMMARY OF FIGURES

FIG. 1a-e shows chemical reactions and catalyst complexes.

FIG. 2 shows selectivity percentages of BHET.

FIG. 3 shows a first reactor set-up (batch type).

FIG. 4 shows a second reactor set-up (flow type).

DETAILED DESCRIPTION OF FIGURES

FIG. 1a shows chemical reactions. Therein poly(ethylene terephthalate)is degraded by using (bmim)FeCl₄ in 1,2-ethanediol. Similar results havebeen obtained with bim and eim. As a result Terephtalic AcidBis(2-Hydroxyethyl) ester (BHET) is formed. Further, it is shown thatBHET can be converted into dimers and oligomers.

FIG. 1b shows a schematic representation of the present catalystcomplex. Therein A represents a nanoparticle, such as maghemite, B abridging moiety directly attached to the nanoparticle such astrisilanolpropyl, and C a catalyst entity, directly attached to thebridging moiety, with C1 being a positive catalyst moiety, such as bim,and C2 being a negative catalyst moiety, such as Cl⁻. If present (hencenot shown) a tail would extent away from the nanoparticle.

FIG. 1c shows a nanoparticle A surrounded by a number of bridgingmoieties and catalyst entities and attached to the nanoparticle.

FIGS. 1d and 1e show reaction equations for formation of the capturecomplex of the invention in accordance with one preferred embodiment. Ina first step (FIG. 1d ) 3-chloropropyl-triethoxysilane is reacted overnight with 1-butyl-imidazole under heating forming a BC sub-complex;herein the butyl may be referred to as a tail. A temperature is from320-470 K, and depending on the temperature a reaction time is from 30min. to overnight. The reaction yields almost 100% BC sub-complex. Theresulting intermediate is the combination of positively chargedN-[3-(triethoxysilyl)propyl]-butylimidazolium and negatively chargedchloride. Subsequently, a Lewis acid, such as FeCl₃ may be added.However, that is not deemed necessary. In a second step, shown in FIG.1e , the ethoxy-groups of the said reaction product thereof areconverted to hydroxyl-groups, to result in a silanol-group. In a thirdstep, that is for instance carried out in water or in ethanol or aqueousethanol, the silanol is reacted with the nanoparticle surface,preferably in the presence of an acid. The resulting capture complex maythereafter be (re)dispersed in the desired solvent for the polymerdegradation, for instance glycol.

It is noted that typically the bridging moiety comprises at one endthereof oxygen comprising entities, such as ethers, alcohols, andcarboxylic acids. Typically these oxygen comprising groups, such as inthe form of an alcohol, are grafted on the present nanoparticle underrelease of water. On another end of the bridging moiety typically atleast one carbon is present, for carrying e.g. a halogenide.

FIG. 2 shows selectivity percentages of BHET (vertical axis), obtainedfrom depolymerization of colored PET, using a maghemite trisilanol bimcomplex with Cl⁻ anions, as function of reaction time and amount ofdi-alcohol (1,2-ethanediol) (horizontal axes). The PET provided was cutinto pieces of about 2×2 cm². In another example pieces of about 0.3×0.3cm², and in a further example as small particles having an averagediameter of 50 μm. The size of the pieces was found to be notparticularly relevant for the outcome. A reaction temperature was about197° C. Results were obtained by varying a reaction time and amount ofdi-alcohol. For all degradation reactions performed, the correspondingPET conversion rates obtained are close to 100% (typically 99-99.99%, asno PET-pieces could be observed anymore in the solvent), which areconsidered to be very high. The selectivity rates (>90%, in a best casescenario so far >93%) are considered to be very high as well. The yieldis as a result also >90%, and up to 93%. Even further the rates areobtained in a relatively short time frame. The selectivities areobtained with 2 wt. % catalyst (including bridging moiety and catalyst)relative to a total amount of polymer, respectively. So a small amountof catalyst is already sufficient.

So despite negative expectations that use of a catalyst complex wouldreduce selectivity, conversion and yield, the present method (andcatalyst complex used therein) provides much better results e.g. inthese respects than prior art methods (using a catalyst per se). Lossesare already reduced from about 20-40% (prior art) to less than 7%.

FIG. 3 shows a batch reactor set-up for a production of about 30 tonBHET per day. A similar set-up exists for a (semi)continuous batchreactor. Therein in an example the solvent:polymer (e.g. ethyleneglycol:PET) mass ratio is 10:1. In another example the ratio is 5:1, andin further example 3:1. The size of the reactor for a residence time of1 minute is about 0.25 m³, and for 30 [min] about 7 m³. So a relativelysmall reactor and a somewhat larger reactor may be used. Both of themare taken to be cylindrical vessels having the following constructionconstraints:

d1:h1=0.5 (diameter versus height)

d2:d1=0.35 (mixer diameter versus diameter)

h2:d1=0.25 (height below mixer versus diameter)

h3:d2=0.2 (height of mixer versus diameter of mixer)

W=d2/5 (width of mixer blade versus diameter of mixer).

Based on these constraint restrictions the following results for reactordesign have been obtained:

Technical Lower Upper Characteristic Value Value Range Volume, [m³] 0.26.0  0.1-10 Diameter (d₁), 0.5 1.5  0.1-3 [m]   Height (h₁), [m] 1.0 3.5 0.5-5 h₂, [m] 0.125 0.525  0.1-1 h₃, [m] 0.035 0.105 0.01-0.5 d₂, [m]0.125 0.375  0.1-0.5 W, [m] 0.0875 0.2625 0.05-0.5

FIG. 4 shows a tube-reactor set-up for a production of about 30 ton BHETper day. For construction thereof in an example carbon steel is used. Amaximum pressure drop in the reactor is found to be 50 Pa/m. In a firstdesign a tube diameter of 8 cm is chosen. The length of the reactor fora residence time of 1 minute is about 20 m, and for 30 [min] about 600m. The minimum pressure drop is found be 10 Pa/m. In a second design atube diameter of 25 cm is chosen. The length of the reactor for aresidence time of 1 minute is about 2 m, and for 30 [min] about 60 m.

Based on these constraint restrictions the following results for reactordesign have been obtained:

Technical Lower Upper Characteristic Value Value Range Volume, [m³] 0.26.0  0.1-10 Diameter (d₁), 0.08 0.25 0.05-0.5 [m] Length (h₁), [m] 2.0600   1-800In order to build a relatively large reactor the design as shown in FIG.4 is taken. On a top side the solvent/polymer (e.g. EG/PET) reactionmixture enters the reactor in an inlet 21. The mixture is distributedover parallel pipes 1-15, located at a front side, and similarly to 15pipes located at a back side (not numbered). The length of the pipe is 4m. After flowing through the pipes, and reacting, the obtained BHETexits the reactor at a bottom side through an outlet 22.

In view of heat transfer characteristics the shorter residence times(e.g. 1 min) can not fulfil the heat requirements or become unpracticalin size. In view thereof the residence time should be (given a requiredthroughput) a minimum of about 5 min, or put otherwise the reactorshould have a bigger volume. A maximum residence time may be limitedpractically by a volume of the reactor smaller (e.g. 8 cm diameterreactor gives a length of >1000 m). In view hereof a tube diameter canbe from 5-50 cm, and a (total) tube length of 1-800 m. The flow rate ispreferably from 0.01 m/s-1 m/s.

In view of various characteristics of the batch-type andflow-type-reactor a combination of the two types provide advantages,such as increased throughput, yield, and reduced energy consumption, byin an example pre-heating and preprocessing in the batch-type (in afirst stage), and finalizing the reaction at a temperature provided bythe batch-reactor (in a second stage).

The reactor may further comprise at least one of a controller, such as apressure controller, a temperature controller, a regulator, a valve, apump, a heater, a cooler, and a sensor.

Both reactor set-ups shown in FIGS. 3 and 4 give similar results foryield etc. as mentioned above. The reactor set-ups also satisfy masstransfer demands, heat transfer demands, and provide adequate mixing,practical constraints, and reasonable flow rates, in view of e.g.temperature, pressure, residence time, and reactant boundary conditions.Despite the limitation still a relatively large degree of design freedomis found to be present.

EXAMPLES

Similar tests as above have been performed on non-colored PET. Theresults thereof are in the same order of magnitude for both conversionand selectivity. As a consequence inventors conclude that a colouradditive has hardly any or no impact in this respect. Even further,additives, such as pigments, can be removed from the degradationproducts, with ease.

Similar tests as above have been performed on a wide range of raw (PET)material, e.g. polyester clothing, PET carpet, PET material fromautomotive industry, recycled PET, multi-layered PET trays containingother polymers, such as PE and PP. The results thereof are in the sameorder of magnitude for both conversion and selectivity, and thus foryield. As a consequence inventors conclude that the process is highlyinsensitive to different raw (PET) material and robust as well.

Similar tests were performed on amorphous (AMP) pellets and solid statepolymerization (SSP) pellets. Again PET conversion and BHET selectivitywere high. Values obtained for SSP pellets were somewhat lower,relatively. It is considered that possibly due to a somewhat longerchain length of the polymer to be degraded selectivity and conversionare somewhat jeopardized.

Further Examples

Examples Found of Degradable Polymers:

Polyesters: PET, PEF, PTT, PLA, polycarbonate

Polyethers: cellulosis

Polyamides: nylon 6

Ionic Liquids Tested:

An imidazolium based functional acid a piperidinium based functionalacid, a pyridinium based functional acid, a pyrrolidinium basedfunctional acid, a sulfonium based functional acid with an additionalside group R3, an ammonium based functional acid with additional sidegroups R3 and R4, and a phosphonium based functional acid withadditional side groups R3 and R4; all with at least side groups R1 andR2 and counter ion X—. X may be selected from F, Cl, Br, I, dicyanamide,bis(trifluoromethyisulphonyl)imide, preferably Cl.

The functional group R1 may be a (mono or multi, 1-4) carboxylic acid,whereas functional group R2 may be an alkane, typically a straight orbranched alkane. Functional groups R3 and R4 may be selected from H, CH3and R1 and R2. Functional groups R1-R4 have been selected independentlyand may be (partly) the same, or not. The side group R2 may have m or ocarbon atoms may be branched, whereas the side group R1 having n(typically 4-20) carbon atoms is preferably straight.

So in summary aromatic and non-aromatic moieties had and have beentested, typically comprising a heteroatom (N, S, P), having a positivecharge on the (or one of) hetero atom(s), and various side groups havebeen tested. The most promising have been claimed, namely the aromaticones with a nitrogen atom.

Metal Salts:

Various metal salt comprising two- or three-plus charged metal ion andnegatively charged counter-ions have been tested, especially Fe, Ca, Co,Mn, and the above counter ions.

Bridging Moiety:

For the bridging moiety weak and functionalize acids have been tested,such as a carboxylic acids and an oxysilane, such as methoxysilane orethoxysilane.

Nanoparticles:

Various nanoparticles have been tested such as having O as counter ion,and Fe, Co and Mn as metal ion, and some combinations thereof. Thesefunction fine.

A size is typically relatively small, hence nanoparticles, with a lowervalue of 2 nm, and an upper value of 500 nm. Both have certain minoradvantages and disadvantages.

Temperature:

Temperatures in the range of 50° C.-500° C. have been found suitable;above about 250° C. pressure needs to be applied.

Pressure:

Pressure from approximately atmospheric to a few bars have been foundsuitable.

Amount of Catalyst:

The amount of catalyst has been tested in a range of 0.1-35 wt. %,relative to a total weight of polymer provided, wherein the lower end ofthe range is considered to be relatively slow, but still applicable forcertain applications, and the higher relatively costly.

Process Time:

Process time varies as a consequence of variations in other parameters;it is studied as such. Reactions are performed up to completion.

Solvent:

The solvent may be any solvent. Good results are obtained with water andalcohols as solvents, in combination with a mono- or di-alcohol. It ispreferred to use the alcohol as claimed.

Reuse of Catalyst:

It has been found that the catalyst can be reused 20-50 times (or more),without significant loss in yield or performance (e.g. less than 1% lessyield after 30 times).

Recovering Catalyst:

Most or all of the catalyst can be recovered easily, depending on themethod of recovery. After 30 times recovery the amount recovered usingmagnetic recovery is higher than 98% of the initial amount, so virtuallyno losses. If filtration is used even higher amounts can be recovered.

Method of degrading a homo or copolymer into oligomers, trimers, dimersand/or monomers, comprising the steps of,

providing the polymer in a suitable solvent, wherein the polymer [seetable, row 1-3] is one or more of a polyester, a polyamide, apolycondensate, and a polyether, wherein the solvent is a mono- ordi-alcohol, the polymer being in solid form,

adjusting temperature and pressure to reaction conditions, wherein thedegrading is performed at a temperature of 50° C.-500° C. [see table,row 4-6],

wherein the pressure is from 90 kPa-10.000 kPa,

providing a catalyst complex comprising a catalyst entity [see table,row 7-8], a magnetic nanoparticle, and a bridging moiety solely betweenthe catalyst entity and the magnetic nanoparticle, the catalyst complexbeing capable of degrading a polyester or polyether polymer intooligomers, trimers, dimers and/or monomers,

wherein the catalyst entity is selected from both partly positive andpartly negative charged moieties,

wherein the positive charge is on an aromatic heterocycle moiety with atleast one nitrogen atom, and

wherein the negative charge is on a metal salt complex moiety having atwo- or three-plus charged metal ion or negatively charged counter-ion,

wherein the magnetic particles have an average diameter of 2 nm-500 nm[see table, row 9-10],

wherein the magnetic particles comprise iron oxide [see table, row11-12],

wherein the bridging moiety is one or more of a weak organic acid,silanol, silyl comprising groups, and silanol, and

wherein the bridging moiety is present in an amount of 5*10-6-0.1 Molebridging moiety/gr magnetic particle,

wherein the amount of catalyst is 0.1-35 wt. %, relative to a totalweight of polymer provided [see table, row 13-15], degrading the polymerover a period sufficient to degrade a significant portion thereof,recovering the catalyst complex, and recycling the recovered catalystcomplex [see table, row 16]

TABLE 1 process parameters of PET depolymerisation Row ParameterResult 1. Polymer: PET flake PET to BHET conversion of 92.4% in 60 min2. Polymer: PTT fiber PTT to BHET conversion of 77.5% in 30 min 3.Polymer: PLA flake All material was decomposed within 120 min 4.Temperature: 197° C. PET to BHET conversion of 92.4% in 60 min 5.Temperature: 185° C. PET to BHET conversion of 88.8% in 180 min 6.Temperature: 175° C. PET to BHET conversion of 12.7% in 240 min 7.Catalyst entity: butyl imidazole PET to BHET conversion of 92.4% in 60min 8. Catalyst entity: 1,4-butyl methyl PET to BHET conversion of 92.0%in 60 min imidazole 9. Size particles: 10 nm PET to BHET conversion of92.4% in 60 min 10. Size particles: 20 nm PET to BHET conversion of82.8% in 75 min 11. Iron oxide: iron oxide, Fe₃O₄ PET to BHET conversionof 92.4% in 60 min 12. Iron oxide: cobalt ferrite, CoFe₂O₄ PET to BHETconversion of 82.8% in 75 min 13. Concentration catalyst complex: PET toBHET conversion of 92.4% in 60 min 20 wt.% Catalyst entity only: 0.4wt.% 14. Concentration catalyst complex: PET to BHET conversion of 88.2%in 90 min 2 wt.% Catalyst entity only: 0.04 wt.% 15. Concentrationcatalyst complex: PET to BHET conversion of 90.2% in 90 min 0.2 wt.%Catalyst entity only: 0.004 wt.% 16. Recovered complex: 20 times PET toBHET conversion with an average 92.9% over 20 subsequent cycles.

Experiment 1: Reference Method (See Table 1, Row 1, 4, 7, 9, 11, and 13)

Experiment 1 is taken as a reference for all other experiments that willbe described in this report. The reference scale of a laboratoryexperiment is 50 g of ethylene glycol (EG) in a 100 mL flask. Thereference mass ratio of the reaction is 1 g of dry catalyst complexparticles:5 g of PET:50 g of EG. The reference catalyst complexcomprises 5 nm magnetite nanoparticles, trisilanolpropyl as bridgingmoiety and as ionic liquid (bim)FeCl₄ or (bmim)FeCl₄). A referencereaction was executed as follows:

The catalyst complex dispersion was homogenised by shaking for 5 minutesby hand. The reference concentration of the catalyst complex dispersionis 10 wt. % of catalyst complex particles in ethylene glycol, thus 10 gof catalyst complex dispersion was taken from the stock dispersion.Subsequently, 41 g of EG was added and the liquids were shortly mixed byhand to homogenise the dispersion. Then, 5 g of PET flakes were addedand the round bottom flask was placed in the heating set up. The heatingwas started and after 20 minutes, the reaction mixture had reached thereaction temperature. The reaction was followed in time by takingin-process-control samples to measure the concentration of BHET producedas a function of time. The concentration of BHET was determined withHPLC. The results of a reference reaction are listed in Table 2.

TABLE 2 Conversion of PET to BHET as a function of time for a referencePET depolymerisation reaction Time PET to BHET conversion [min] [%] 51.7 10 5.4 15 10.0 20 10.5 35 31.8 45 51.5 60 92.4

Experiment 2: Type of Polyester (See Table 1, Row 1-3)

The experiment was executed as experiment 1, but instead of 5 g of PETflakes, 5 g of PTT fiber (experiment 2a) or 5 g of PLA flakes(experiment 2b) was added. The results are listed in Table 3.

TABLE 3 Conversion of a polyester to BHET PET to BHE Time conversionExperiment Material [min] [%] 1 PET 60 92.4 2a PTT 30 77.5 2b PLA 120All flakes decomposed

Experiment 3: Temperature (See Table 1, Row 4-6)

The temperature was lowered to 185° C. (experiment 3b) and 175° C.(experiment 3a). The composition of the reaction mixture was equal toexperiment 1. The results are listed in Table 4.

TABLE 4 Conversion of PET to BHET as a function of temperature ReactionPET to BHET Temperature time conversion Experiment [° C.] [min] [%] 3a175 240 12.7 3b 185 180 88.8 1 197 60 92.4

Experiment 4: Catalyst Entity (See Table 1, Row 7-8)

In the catalyst complex preparation, the catalyst entity and bridgingmoiety were replaced by butyl-methylimidazolium. The PETdepolymerisation method was unchanged. The results are listed in Table5.

TABLE 5 Conversion of PET to BHET by different catalyst entitiesReaction PET to BHET time conversion Experiment Catalyst entity [min][%] 1 Butylpropyl 60 92.4 imidazolium 4 butylmethyl 60 92.0 imidazolium

Experiment 5: Nanoparticle Oxide and Particles Size (See Table 1, Row9-12)

In the catalyst complex preparation, the nanoparticle was replaced bycobalt ferrite instead of magnetite. As a result, also the size of theparticle increased on average from 10 nm to 22 nm. The PETdepolymerisation method remained unchanged. The results are listed inTable 6.

TABLE 6 Conversion of PET to BHET by different functionalisednanoparticles Average Reaction PET to BHET size time conversionExperiment Nanoparticle [nm] [min] [%] 1 Magnetite 10 60 92.4 5 Cobalt22 75 82.8 ferrite

Experiment 6: Concentration of Catalyst Complex (See Table 1, Row 13-15)

A lower concentration of the catalyst complex was used: instead of 20wt. % relative to the weight of the polymer, now 2 wt. % (experiment 6a)and 0.2 wt. % (experiment 6b) were used. The PET depolymerisation methodremained unchanged. The results are list in Table 7.

TABLE 7 Conversion of PET to BHET as a function of catalyst complexconcentration Wt. % PET to BHET catalyst Time conversion Experimentcomplex [min] [%] 1 20 60 92.4 6a 2 90 88.2 6b 0.2 90 90.2

Experiment 7: Recyclability of the Catalyst Complex (See Table 1, Row16)

The recyclability of the catalyst complex was tested by recycling thecatalyst complex 20 times. This was done by executing the reference PETdepolymerisation method, cooling down the reaction mixture andseparating the catalyst complex using a magnet. In this way, a catalystcomplex-free supernatant remained, was decanted. The catalyst complexwas redispersed in fresh EG such that the reference mass ratio wasobtained and the reference method was repeated. This process wasrepeated such that the catalyst complex was used 20 times, thus recycledfor 19 times. The average process yield was 92.9%.

Experiment 8: Concentration of EG

The concentration of EG in the reaction mixture was changed with respectto the reference method of 1 catalyst complex:5PET:50EG to 1 catalystcomplex:5PET:25 EG (experiment 8a) and 1 catalyst complex:5PET:100EG(experiment 8b). The amount of EG in the reaction mixture was keptconstant, the amount of catalyst complex and PET were changed. Theresults are listed in Table 8.

TABLE 8 Conversion of PET to BHET as a function of EG concentration Massratio Reaction PET to BHET catalyst time conversion Experiment complexPET EG [min] [%] 8a 1 5 25 75 91.2 1 1 5 50 60 92.4 8b 1 5 100 120 75.0

Experiment 9: Free Ionic Liquid Vs. Bound Ionic Liquid

Instead of the catalyst complex, the free catalyst entity was used,butyl imidazole. The catalyst entity solely was used in the same massratio, thus 1 catalyst entity:5 PET:50 EG (experiment 9a). In order tocompare the performance of the free catalyst entity in a similarconcentration on the catalyst complex as in the reference PETdepolymerisation method, the mass ratio 0.02 catalyst entity:5 PET:50 EG(experiment 9b) was performed. The results are listed in Table 9. Notethat experiment 9a effectively uses about 50 times more catalyst thanexperiment 1. When compensated for this ratio (experiment 9b) thereaction time is much longer (160 versus 60 minutes) and the yield ismuch lower (20%). The present catalyst complex is thus much moreeffective.

TABLE 9 Conversion of PET to BHET as a function of unbound catalystentity concentration Mass ratio Complex or Reaction PET to BHET entitytime conversion Experiment only PET EG [min] [%] 1 1 5 50 60 92.4 9a 1 550 45 85.9 9b 0.02 5 50 160 73.9

Experiment 10: Preparation of a Catalyst Capture Complex

Preparation of the Linker-Catalyst Complex (Bridge-Catalyst)

An alkyl imidazole (bim) is mixed with a halogensilane(triethoxysilylpropyl chloride) in a 1:1 molar ratio and stirred at aslightly elevated temperatures for 8 hours.

Preparation of the Catalyst Complex

The magnetite nanoparticles are prepared based on the method firstdescribed by Massart et al. in 1981:

An Fe(II) solution is mixed with a Fe(III) solution in a 1:2 molar ratiorespectively. The iron oxide nanoparticles are formed by aco-precipitation reaction in basic medium while stirring. Subsequently,the resulting iron oxide particles are washed water and ethanol.

Next, an adequate amount of linker-catalyst complex diluted with ethanolis mixed well with the dispersion of iron oxide particles, after whichammonia added. The reaction mixture is stirred for 15 hours.

The particles are washed with acetone prior to redispersion in ethyleneglycol.

Experiment 11

PET depolymerisations using the present flow system.

A. Parameter Settings

Temperature Initial Chemicals

PET/EG premix>313° K (>40° C.)

Magnetic Fluid>313° K (>40° C.)

Flow-Rate

50 ml/min

Residence Time

5 minutes at 453° K (180° C.)

Heat Up

Mixture was heated from 313° K (40° C.) to 453° K (180° C.) in the coiland still had an average residence time of 5 minutes at 453° K (180°C.).

The depolymerization was performed successfully. A fully pumpabledispersion of PET in EG was achieved. Also homogeneous mixing ofMagnetic fluid and PET/EG premix was established. The experimentresulted in a safe setup that does not clog. The depolymerisationmeasured in the reaction using HPLC gave >90% yield, as usual.

It is noted that with HPLC one can determine the amount of BHET formedin the reaction.

Sampling

For sake of comparison sampling was performed at the beginning of theprocess, in the PET/EG premix, and at the end of the process when theliquid came out of the coil.

Results

Full PET to BHET conversion was achieved.

The invention although described in detailed explanatory context may bebest understood in conjunction with the accompanying examples andfigures.

It should be appreciated that for commercial application it may bepreferable to use at least one variations of the present system, whichwould similar be to the ones disclosed in the present application andare within the spirit of the invention.

The invention claimed is:
 1. Improved method of degrading a polymerbeing a homo or copolymer into oligomers, trimers, dimers and/ormonomers, comprising the steps of providing the polymer in a suitablesolvent in a reactor, the polymer being in solid form, adjustingtemperature and pressure to reaction conditions, providing a reusablecatalyst complex being capable of degrading the polymer into oligomersand/or monomers, the polymer, solvent and catalyst complex forming adispersion, and degrading the polymer over a period sufficient todegrade a significant portion thereof, and recovering the catalystcomplex, characterized in that the polymer is supplied in the form of aproduct with an average volume of 10⁻⁷-50 cm³, wherein a polymerconcentration in the dispersion is from 1-30 wt. %, wherein an averageresidence time of the polymer in the reactor is from 30 sec.-3 hours,wherein the catalyst complex comprises a catalyst entity, a magneticnanoparticle, and a bridging moiety solely between the catalyst entityand the magnetic nanoparticle, the catalyst complex being capable ofdegrading a polymer into oligomers, trimers, dimers and/or monomers,wherein the catalyst entity comprises an aromatic heterocycle moietyhaving a positive charge and a moiety having a negative charge, whereinthe catalyst entity and bridging moiety are attached, and wherein thebridging moiety and nanoparticle are attached, wherein the magneticparticles have an average diameter of 2 nm-500 nm, and wherein thebridging moiety is present in an amount of 5*10⁻⁶-0.1 Mole bridgingmoiety/gr magnetic particle, and wherein the reactor is selected from a(semi)continuous type, such as a continuous stirred tank reactor (CSTR),and a tube-like reactor, such as a loop reactor, a plug flow reactor, anoscillatory flow reactor, an N-unit loop reactor system, and a batchtype, and combinations thereof.
 2. Method according to claim 1, whereindegrading of the polymer is performed in at least two stages, in thefirst stage the polymer is pre-treated, and in a second stage thedegradation is completed.
 3. Method according to claim 2, wherein anaverage residence time of the polymer in the second degradation stage is10 sec-60 min.
 4. Method as claimed in claim 2, wherein the first stageis carried out in a vessel provided with a mixer.
 5. Method as claimedin claim 2, wherein heat is provided in the first stage by means ofsteam.
 6. Method as claimed in claim 2, wherein the second stage iscarried out in a plug flow reactor.
 7. Method as claimed in claim 6,wherein the plug flow reactor is embodied as a plurality of tubesarranged in parallel.
 8. Method as claimed in claim 1, wherein theplastic comprising the polymer is reduced in size to arrive at thespecified volume.
 9. Method according to claim 1, comprising at leastone steps selected from recovering the catalyst attached to the magneticparticle, recycling the recovered catalyst complex, removing additivesfrom the solvent, providing oligomers to the solvent, adjusting anamount of negative charged molecules, and retrieving trimers, dimers,and/or monomers.
 10. Method according to claim 1, wherein the polymer isat least one of a polyester, a polyether, a polyamine, a polyamide and apolycondensate.
 11. Method according to claim 1, wherein the solvent isa reactant, the reactant being capable of reacting with the polymerbeing degraded.
 12. Method according to claim 1, wherein the aromatichetero-cycle comprises at least two nitrogen atoms.
 13. Method asclaimed in claim 12, wherein the bridging moiety further comprises alinking group, via which it is coupled to the aromatic heterocycle. 14.Method according to claim 2, wherein the polymer and solvent areprovided at a temperature of 15-30° C., wherein in a first stage thetemperature is increased to 170-200° C., and wherein in a second stagethe temperature is maintained at 170-200° C.
 15. Method according toclaim 1, wherein the polymer is polyethylene terephthalate (PET) orpolyethylene furanoate (PEF), the solvent is ethanediol, the catalystcomprises butylimidazolium (bim⁺) and Cl⁻ or FeCl₄ ⁻, the bridgingmoiety is triethoxysilylpropyl, the amount of catalyst is 0.1-20 wt. %,the degrading is performed at a temperature of 90° C.-250° C., and thenanoparticle is at least one of magnetite, hematite, and maghemite. 16.The method of claim 1 wherein the catalyst entity and bridging moietyare attached by a chemical covalent bond.
 17. The method of claim 1wherein the bridging moiety and nanoparticle are attached by a covalentbond.